Radioopaque compounds and methods of preparing the same



United States Patent 3,360,436 RADIOOPAQUE COMPOUNDS AND METHODS OF PREPARING THE SAME Ernst Felder and Davide Pitre, Milan, Italy, assignors to Eprova Limited, Schaffhausen, Switzerland No Drawing. Filed Nov. 12, 1963, Ser. No. 323,085 Claims priority, application Switzerland, Nov. 23, 1962, 13,788/ 62; Aug. 9, 1963, 9,857/ 63 24 Claims. (Cl. 167-95) They also affect certain aspects of human metabolism for extended periods.

The primary object of the invention is the provision of contrast media which are better tolerated than known iodine bearing contrast media.

More specifically, the invention aims at providing radioopaque substances which do not tend to be bound to protein in the body, and which are well tolerated for this reason.

Another object is the provision of radioopaque substances which are rapidly excreted by the urinary tract.

The compounds of the invention which achieve the afore-mentioned objects have the formula (IJOOX R-NH(|JH- NH-R wherein R and R are lower alkanoyl radicals, R" is either hydrogen or lower alkyl, and X may be hydrogen, low-er alkyl, a physiologically tolerated alkali metal, or a physiologically tolerated organic base, such as akanolarnin-e. The several radioopaque compounds of the invention may be employed in mixtures with each other. R and R may be identical, or they may be different lower alkanoyl radicals.

The alkali metal salts of the triiodobenzoic acid derivatives of the invention have very high solubility in water, and salts of certain organic bases are even more soluble. The readily water soluble salts of the invention are therefore suitable for urography or angiography, including the preparation of cerebral angiograms. Other body cavities which are more accessible from the outside than the kidneys or the blood vessels may be instilled with suspensions of the water insoluble esters of the invention. Formulations based on water insoluble radioopaque compounds of the invention may thus be employed forsalpingography, and particularly for bronchography:

The radioopaque compounds of the invention are distinguished by their chemical inertness which makes them stable, and causes them to be well tolerated by-living organisms. Even when employed intravenously in high dos- 3,360,436 Patented Dec. 26, 1967 ages, the radioopaque compounds of the invention do not lower the blood pressure, but produce a slight rise in blood pressure. The danger of circulatory collapse, always present in intravenous application of contrast media, is thus significantly reduced. The compounds of the invention have not been found to have the unfavorable effects on breathing observed with some clinically useful contrast media.

The intracerebral toxicity of the compounds of the invention is particularly low, and this property makes them eminently suitable for cerebral angiography. The compound-s, when applied by intravenous injection as is customary in urography and angiography, are practically completely excreted in a very short period.

Slow or incomplete secretion is undesirable because it reduces the contrast of X-ray pictures taken of the urinary tract. Moreover, and even more important, the iodine storage function of the thyroid gland is adversely affected by iodine bearing radioopaque compounds, and the extent of this undesirable side effect is inversely related to the rate of excretion of the contrast medium.

Because of the readily observed favorable effects of the contrast media of the invention on blood circulation and breathing, it is reasonable to assume that the long term side effects of the compounds, if any, will be relatively small. The rarer types of side effects and the long range after effects of contrast media cannot readily be observed in clinical tests on an experimental scale. The clinical tests available so far confirm the favorable results of the conventional pharmacological tests performed prior to application to human patients.

The following table shows a comparison of test results obtained with 3acetylaminomethyl-5-acetylamino-2,4,6- triiodobenzoic acid, a typical compound of this invention, and with 3,5-diacetylamino-2,4,6-triiodobenzoic acid which is a well known and clinically proved radioopaque material. It will be noted that the two compounds differ by a CH radical which in the compound of the invention is interposed between the benzene nucleus and a nitrogen atom. The compounds, therefore, are not members of the same homologous series.

Effect on bronchial tonus Excretion with urine in percent of i.v. doses of 100-200 mg./kg.:

After 30 minutes g. Distinct increase;

After one hour 4. After three hours Solubility of Na salt in water 54.1.

in grams per milliliters at 22 0.

The invention 1s also concerned with methods of preparing the novel triiodobenzoic acid derivatives of the invention. There is no known sequence of steps for synthesizing the compounds. We have developed methods 3 which permit the radioopaque compounds of the invention to be produced in relatively few steps, and with good overall yields.

The starting material for the method of the invention is a compound of the formula C O OH (II) wherein Y and Y are hydrogen or a substituent which is readily exchanged against hydrogen, such as halogen, and more specifically chlorine. The compound of Formula II is reacted in the presence of a strong acid with an N-hydroxymethyl-acylamide to form the compound Monoand dichloroacetyl radicals are preferred acyl radicals, but it will be appreciated that the chemical nature of the acyl radical introduced with the N-hydroxymethylacylamide and subsequently removed by hydrolysis is not critical.

Nitration of the compound (IV) yields NH2-CHz N02 which is then acylated by means of a compound R-Z wherein R represents a lower alkanoyl radical as in Formula I, and Z is a radical capable of reacting with a hydrogen atom of the amino radical in Formula V. Oxygen or halogen are typical representatives of Z. The acylation product has the formula and is hydrogenated, for example, by molecular hydrogen in the presence of a catalyst, to produce the compound R-NII-CH N H:

C O O H (VII) If Y or Y are halogen, they may be simultaneously exchanged for hydrogen in the hydrogenation step, and chlorine should be so exchanged. If Y or Y is iodine, the hydrogenation may readily be controlled to avoid removal of iodine.

COOH

which is further acylated with RZ to produce (VIII) a typical radioopaque compound of this invention.

It Will be appreciated that the sequence of the steps outlined above may be altered to some extent. Particularly, the sequence of steps leading from compound (V) to compound (IX) may be rearranged in many ways. The two acylating steps may be combined as a terminal operation, whereby R and R become identical. If the acyl radical of the N-hydroxymethyl-acylamide is R, the hydrolysis reaction leading to compound (IV) and the subsequent acylation leading from compound (V) to compound (VI) are unnecessary. If RZ is employed in excess in the last step of the sequence of reactions outlined above in more detail, R may be replaced by R in the following sequence of reactions:

We have found that 4-halobenzoic or 2,4-dihalobenzoic acids are preferable to benzoic acid as starting materials for theabove sequence of reactions. The presence of at least one halogen atom in position 4 of the benzene nucleus appears to influence nitration in such a manner that only the desired S-nitro substitution product is formed. In the absence of halogen in position 4, appreciable amounts of the corresponding 4-nitro substitution product are obtained and reduce the yield. Separation of the two isomeric nitration products also is not easy.

The chlorinated derivatives of benzoic acid are practically unaffected .by hydrolyzing agents, whereas the corresponding iodobenzoic acids are less stable. If 2-iod0- benzoic acid, 4-iodobenzoic acid, or 2,4-diiodobenzoic acid are employed as starting materials, the amount of reagent required in the iodation reaction leading to compound (VIII) is correspondingly reduced, thus compensating for loss of material in hydrolysis steps.

The preferred iod-ating agent of the invention is potassium iodochloride, KICL but it will be understood that iodine chlorides such as 1G1 and complex compounds thereof other than KICl may be employed as well.

The following examples are further illustrative of the present invention, and it will be understood that the invention is not limited thereto:

Example 1 100 grams 4-chlorobenz0ic acid and 165 grams N hydroxymethyl-dichloroacetamide were st rred consecutively at room temperature into 1,000 milliliters concentrated sulfuric acid. The mixture was left standing for six days at ambient temperature. It was then gradually adm xed with agitation to 2.5 kilograms crushed ice. A precipitate formed in the aqueous mixture. It was filtered off with suction, washed with water, dissolved in sodium 'bicar bonate solution, and precipitated from the latter with hydrochloric acid.

The purified precipitate weighed 163 grams (80 percent of theoretical yield). It was recrystallized from 50 percent ethanol and identified as 3-dichloroacetyla ninomethyl-4-chlorobenzoic acid having a melting point of 190 C. to 191 C. The equivalent weight was determined experimentally to be 295.2 in close approximation to the theoretical value of 296.45.

300 grams crude 3-dichloroacetylaminoethyl-4-chlorobenzoic acid prepared in the manner described abovewere refluxed for three hours in -a mixture of 1700 milliliters concentrated hydrochloric acid, 500 milliliters glac al acetic acid, and 1,300 milliliters water. The reaction mixture was filtered while hot, and the filtrate was permitted to cool to room temperature. A crystalline precipitate was formed. It consisted of the hydrochloride of 3-ami nomethyl-4-chlorobenzoic acid. M.P. 284-286 C. Yield 174 grams'(78%). U

The hydrochloride was suspended in 1,800 milliliters water. The suspension was heated to 55 -60 C., whereby the solid material was dissolved. When a solution of 31.5 grams sodium hydroxide in 180 milliliters water was added, the free 3-aminomethyl-4echlorobenzoic acid was precipitated in the form of white crystals. A small amount of acetic acid was added to the reaction mixture, whereupon the crystals were filtered oil with suction and dried. M.P. 288290 C. Yield 133 grains (90%).

A nitrating acid was prepared by dropwise addition of 28.6 milliliters nitric (sp. gr. 1.52) to 240 milliliters sulfuric acid monohydrate at to 5 C. 64 grams 3-aminomethyl-4-chlorobenzoic acid were added in small batches to the nitrating acid the temperature of which was kept at 45 to 50 C. The mixture was held at 50 to 55 C. for three hours, and was then carefully poured over 1.5 kilograms ice. The precipitate formed in the aqueous system was filtered off with suction, and dissolved in a mixture of 70 milliliters concentrated sodium hydroxide solution and 500 milliliters water. The temperature of the solution was raised to 40 C., and 40 milliliters acetic anhydride were admixed. The mixture was left to stand for some time, then cooled to room temperature. The precipitate formed was separated from the liquid and dried. There were obtained 69 grams 3-acetylaminomethyl-4- chloro-S-nitrobenzoic acid (73% of theoretical yield). When recrystallized from ethanol, the acid had a melting point of 214216 C. Its equivalent weight was found to be 271.5 in good agreement with the theoretical value of 272.65.

65.4 grams (0.24 mole) 3-acetylaminomethyl-4Fchloro-5-nitrobenzoicacid were dissolved in a mixture of 48 milliliters N sodium hydroxide and 1,800 milliliters water. 12 grams of a 10% palladium catalyst on a carbon carrier were added, and the nitro'benzoic acid derivative was hydrogenated at slightly elevated temperature and at atmospheric pressure. The hydrogen was avidly absorbed. The nitro group Was fully reduced to the corresponding amino radical within about 20 to 40 minutes, and 99 to 100 percent of the amount of chlorine ions to be theoretically expected was formed. Hydrogen absorption then stopped.

The catalyst was removed by filtration. The filtrate was diluted to about 18 liters, and was acidified with 15 milliliters concentrated hydrochloric acid. With vigorous stirring, 1152 milliliters N KICl solution were run into the diluted filtrate over a period of about 20 to 30 minutes. A solid precipitate was formed, and Was filtered off after about six hours. The solid material was washed with water, with sodium bisulfite solution, and again with water. It was dissolved in aqueous ammonium hydroxide solution, the solution was filtered, and the filtrate was acidified with concentrated hydrochloric acid containing a small amount .of sodium bisulfite. After a short time, the precipitate formed was filtered with suction, washed with water, and dried.

There were obtained 109' grams 3-acetylaminomethyl- 5-aniino-2,4,6-triiodobenzoic acid which decomposes and melts at approximately 230 C. The equivalent weight was determined experimentally as being 591, as compared to a theoretical value of 586.

A suspension of 40 grams 3-acetylaminomethyl-5- amino-2,4, '6-triiodobenzoic acid in 180 milliliters acetic anhydride were mixed with 0.4 milliliter concentrated sulfuric acid. An exothermic reaction was thereby initiated. Acetylation was completed by heating to C for three hours.

The reaction mixture was then evaporated to dryness in a vacuum at a temperature not exceeding 50 C. The residue was treated with a mixture of 30 milliliters concentrated aqueous ammonium hydroxide and 40 milliliters water, whereby the solid material dissolved with spontaneous heating. Within a few minutes, the ammonium salt of the acetylated product started precipitating. The precipitate and residual liquid were cooled externally with ice after about 15 minutes. The salt was separated from the liquid by filtration with suction, and was washed with ice cold saturated ainmonium chloride solution.

The salt was dissolved in 300 milliliters water, and insoluble matter was removed from the solution by filtration. The free acid was precipitated from the filtrate at 50 to 60 C. by the addition of 40 milliliters 1:1 hydrochloric acid. The precipitate was filtered oif after a few hours, washed with water, and dried. There were obtained 34 grams 3-acetylaminomethyl-5-acetylamino- 2,4,6-triiodobenzoic acid (79% of theoretical yield) having a melting point of 2'46-248 C. The equivalent weight of this practically pure acid was found to be 631 as compared to the calculated value of 627.96.

When recrystallized from glacial acetic acid, the pure acid melts at 255257 C. It was further identified by partial elementary analysis:

Calculated: N, 4.47%; I, 60.75%. I, 60.48%.

3-acetylaminomethyl 5 acetylamino 2,4,6 triiodobenzoic acid is only sparingly soluble in water. The solubility at 22 C. is 0.3 gram per milliliters water.

Found: N, 4.55%;

Example 2 Salts and esters of 3-acetylaminomethyl 5 acetylamino-2,4,6-triiodobenzoic acid are readily prepared by conventional methods.

The sodium salt is obtained by dissolving the free acid in an equivalent amount of aqueous sodium hydroxide solution. The solubility of the salt at ambient temperature is approximately 80 grams per 100 milliliters water. Sterile solutions ofthe sodium salt in concentrations of 20 to 70 percent may be injected as contrast media for urography and arteriography in the conventional manner.

They also outline the contours of other body cavities into which the solutions are introduced.

The N-methylglucamine salt of 3-acetylaminomethyl- S-acetylamino 2,4,6 triiodobenzoic acid is obtained by dissolving equivalent amounts of acid and base in water. The N-glucosamine salt is miscible with water in almost all proportions. Aqueous solutions containing 90% of the salt can be prepared in the manner indicated. Injectable solutions containing about 20 to 90 percent of the salt are well suited for urography and arteriography.

The lithium salt is prepared by reacting the free acid with the equivalent amount of lithium hydroxide. A lithium hydroxide solution was prepared from 4.2 grams lithium hydroxide and approximately 100 milliliters water. 62.8 grams 3-acetylaminomethyl acetylamino- 2,4,6-triiodobenzoic acid were dissolved in the aqueous lithium hydroxide solution. The lithium salt is freely soluble in water. It may be employed either singly or in mixture with the other salts as a contrast medium for urography, arteriography, or for visualizing other body cavities under X-rays.

Equivalent amounts of the free acid and of high-purity diethanolamine in the presence of a little water from the diethanolamine salt which is miscible with water in almost all proportions. The diethanolamine salt is readily tolerated, and is a useful contrast medium.

Various conventional methods may be employed for preparing the esters of lower alkanols with 3-acetylaminomethyl 5 acetylamino 2,4,6 triiodobenzoic acid. The methyl ester which melts at approximately 230 C. is conveniently obtained by reacting the acid with diazomethane.

An ether solution of diazomethane was prepared in the conventional manner by alkaline degradation of 4.5 grams toluenesulfonyl-nitrosomethylamide. It was combined with a suspension of 6.3 grams 3-acetylaminomethyl 5 acetylamino-2,4,6-triiodobenzoic acid in 50 milliliters ether. After 24 hours, the reaction mixture was filtered, and the precipitate was washed first with dilute sodium bicarbonate solution, and then with water. 5.4 grams of the methyl ester were obtained. The ester is insoluble in water, ethyl acetate, and ethyl ether, but soluble in Warm methanol, acetone, and very readily soluble in dioxane.

The esters of homologous alkanols may be prepared in a manner analogous to the aforedescribed preparation of the methyl ester, or by a method patterned on the following method of preparing the ethyl ester:

A solution of 3 grams sodium in 250 milliliters ethanol was mixed with 63 grams 3-acetylaminomethyl- 5-acetylamino-2,4,6-triiodobenzoic acid and with 18 grams diethyl sulfate. The mixture was refluxed for six hours. After subsequent cooling, it was stirred into one liter 5% aqueous sodium bicarbonate solution. A precipitate formed. It was recovered by filtration and washed. The ethyl ester so obtained has a melting point of 220-222 C. It is insoluble in water and ether, but is readily soluble in warm acetone, and very freely soluble in dioxane and in boiling ethanol.

Example 3 The method of Example 1 may be modified in many details as to sequence of steps, reaction conditions, and reagents without affecting the results obtained. The homologs of 3-acetylamidomethyl 5 acetamido 2,4,6 triiodobenzoic acid are obtained in an analogous manner by substituting equivalent amount of homologs for certain reagents as will be apparent from the following description of the preparation of 3-propionylaminomethyl-5- propionylamino-2,4,6-triiodobenzoic acid.

50 grams crude 3-aminomethyl-4-ch1orobenzoic acid were nitrated in the manner of Example 1 by means of a mixture prepared at 0 C. from 22.4 nitric acid (sp. gr. 1.52) and 188 milliliters concentrated sulfuric acid. The neutral sulfate monohydrate of 3-aminomethyl-4-chloro-5-nitrobenzoic acid was obtained as a precipitate insoluble in ice cold water, and was recrystallized from water. Its melting point is 247-249 C., the yield was 75 grams. The free acid was prepared from the sulfate by dissolving the latter in aqueous sodium hydroxide solution and by acidifying the solution of the sodium salt with acetic acid.

There were obtained 49 grams 3-aminometl1yl-4-chloro- S-nitrobenzoic acid having a melting point of 243-246" C., an equivalent weight of 231.2 when determined by HClO titration, and 230.8 when determined by NaOH titration. The calculated equivalent weight is 230.5.

46 grams 3-aminomethyl-4-chloro-S-nitrobenzoic acid were dissolved in 1200 milliliters water containing 8 grams sodium hydroxide. The solution was heated to 40 C., and 29 grams propionic anhydride were admixed. The mixture was stirred for three hours at 50 C. Cooling and acidification with hydrochloric acid resulted in the precipitation of 3-propionylam-inomethyl-4-chloro-5-nitrobenzoic acid. The yield was 44 grams (77%). A sample recrystallized from much water melted at 181 C. The equivalent weight was found to be 286 as compared to a calculated value of 286.67.

57 grams (0.2 mole) 3-propionylaminomethyl-4-chloro- 5-nitrobenzoic acid prepared in the manner indicated above were dissolved in 1500 milliliters water containing 16 grams sodium hydroxide, and were hydrogenated in the presence of 7 grams of a catalyst consisting of 10% palladium on a carbon support. After completion of hydrogen absorption, the catalyst was removed by filtration. The filtrate was diluted to 12,500 milliliters, and was acidified with hydrochloric acid. While the diluted solution was vigorously agitated, it was gradually mixed with 610 milliliters 1 N KIC1 solution. Agitation was continued for 14 hours at room temperature. The precipitate formed was filtered off, washed with dilute sodium bisulfite solution, dissolved in dilute aqueous ammonium hydroxide solution, and reprecipitated with hydrochloric acid. The 3 propionylaminomethyl-S-amino 2,4,6 triiodobenzoic acid was filtered from the mother liquor with suction, washed with water and dried. It weighed 91 grams (76% yield), melted at 230 C. with decomposition, and had an equivalent weight of 599 (calculated 599.97).

32 grams 3-propionylaminomethyl-5-amino-2,4,6-triiodobenzoic acid were suspended in 60 milliliters propionic anhydride. The suspension was heated to 60 C. with agitation. 12 milliliters sulfuric acid were added, and the mixture was held on a steam bath for three hours. A clear solution was initially formed, and the propionylated product later crystallized. The mixture was left to stand overnight, whereafter the crystalline precipitate was recovered by filtration with suction, and washed with ether. It was then dissolved in a solution of 6 grams sodium bicarbonate in milliliters water. A small amount of insoluble material was removed by filtration, and the filtrate was acidified with hydrochloric acid to precipitate 3-propionylaminomethyl-5-dipropionylamino 2,4,6 triiodobenzoic acid. The acid was filtered off, washed with water, and dried. It weighed 28 grams and had a melting point of 226-228 C. The equivalent found was 712 (calculated 712.19).

The acid was dissolved in a mixture of 84 milliliters N sodium hydroxide solution and milliliters water, and the alkaline solution was kept at 60 C. for six hours with stirring. It was then acidified to precipitate 3-propionylaminomethyl 5-propionylamino-2,4,6-triiodoberlz0ic acid. The latter acid was isolated by filtration, washed, and dried. As recovered, it weighed 24 grams and had a melting point of 183-185 C. After recrystallization from 95% ethanol, the pure acid was obtained and had a melting point of 234-235 C. The equivalent weight found by titration was 658 (calculated 656.04).

The acid is only sparingly soluble in water, but it is soluble in warm methanol and ethanol. Its sodium and N-methylglucamine salts are readily soluble in water and are useful contrast media for urography, angiography, and the X-ray examination of other body cavities.

Example 4 When 69 grams 3-aminomethyl-4-chloro-5-nitrobenzoic acid obtained as described in Example 3 were reacted with 52.5 grams butyric anhydride in the manner apparent from Examples 1 and 2, there were obtained 60 grams (0.2 mole) 3butyrylaminomethyl-4-chloro-5-nitrobenzoic acid having a melting point of 197 C. The equivalent weight was found to be 301 (calculated 300.7).

The product was hydrogenated in the manner described in Example 3, and the hydrogenated compound was treated with KlCl There were obtained 92 grams 3-butyr ylaminomethyl--amino-2,4,6-triiodobenzoic acid which melted under decomposition at 218 C. The equivalent weight found Was 611 (calculated 614).

Reaction with butyric anhydride and partial hydrolysis with sodium hydroxide in a manner analogous to the method of Example 3 yielded 3-butyrylarninomethyl-5- butyry1amino-2,4,6-triiodobenzoic acid having a melting point of 189 to 190 C.

Example 5 The same compound as in Example 4 was prepared from 3 acetylaminomethyl-5-amino-2,4,6-triiodobenzoic acid. The acetyl radical was replaced by a butyryl radical by treatment with butyric anhydride, and other homologs of 3-acetylaminomethyl-S-acetyl-amino-Z,4,6-triiodic acid may be prepared in an analogous manner.

29.2 grams (0.05 mole) 3-acetylaminomethyl-S-amino- 2,4,6-triiodobenzoic acid were suspended in 120 milliliters butyric anhydride. The suspension was heated to 60 C., and 0.3 milliliter concentrated sulfuric acid were added to initiate an exothermic reaction. A temperature of 90 C. Was maintained for three hours. The starting materials first formed a homogeneous solution whereafter a precipitate was formed. The latter was filtered off, and was washed with ether. It was then dissolved in sodium bicarbonate solution and reprecipitated with acid. 27.5 grams 3-N-acetyl-N-butyryl-amino-methyl 5 butyrylamino-2,4,6-triiodobenzoic acid having a melting point of 210-212 C. were recovered. The iodine content was found to be 52.14% (calculated 52.44%

27 grams of the last mentioned acid were suspended in 200 milliliters water, and were dissolved in the liquid by the addition of a solution of 1.5 grams sodium hydroxide in milliliters water. The solution was heated to 65 C., and a solution of 1.2 grams sodium hydroxide in milliliters water was added in small batches. Ultimately, 80 grams sodium chloride were added, and the solution was cooled to room temperature. A small amount of precipitate formed, and was removed by filtration. The filtrate was diluted with much water, and was strongly acidified with hydrochloric acid. A voluminous precipitate was formed. It was filtered off with suction, and dried. The crude product was identified as 3-butyrylaminomethyl-5-butyrylamino 2,4,6 triiodobenzoic acid having a melting point of 189 to 190 C. (decomposition). The equivalent weight was found as 690 (calculated 684.1).

Elementary micro-analysis: Calculated for N, 4.09%; I, 55.66%. Found: N, 3.92%; I, 56.23%.

When recrystallized from 95% ethanol, the free acid melted at 221-224 C.

The acid is only sparingly soluble in water, but is soluble in lower alkanols, chloroform, and acetic acid, particularly at elevated temperature. Its sodium and N- methylglucamine salts are readily Water soluble.

Example 6 3-acetylaminomethyl-S-acetylamino 2,4,6 triiodobenzoic acid and its homologs may also be prepared from 10 4,6-dihalobenzoic acid in the following sequence of reactions:

grams 4,6-dichlorobenzoic acid were dissolved in 1150 milliliters concentrated sulfuric acid (sp.gr.1.84). While the solution was being agitated, 142 grams N-hydroxymethyl-dichloroacetamide were gradually added over a period of one hour. The reaction mixture was stirred for two days at room temperature, and was then mixed With 4 kilograms ice. The precipitate formed in the aqueous medium was filtered with suction, washed, dissolved in sodium bicarbonate solution, and reprecipitated with hydrochloric acid. There were obtained 195 grams 3-dichloroacetylaminomethyl-4,6 dichlorobenzoic acid having a melting point of 199 C. (97.5% yield). The equivalent weight found was 333 (calculated 330.99). The acid may be recrystallized from 70% aqueous ethanol.

100 grams 3-dichloroacetylaminomethyl-4,6-dichlorobenzoic acid were refluxed in a mixture of 900 milliliters 18% aqueous hydrochloric acid and 180 milliliters glacial acetic acid for four hours. When the reaction mixture was permitted to cool, a white precipitate was formed. It was recovered by filtration, and was washed with ether. There were obtained 60.5 grams (78% yield) of the hydrochloric acid addition salt of 3-aminomethyl-4,6-di chlorobenzoic acid having a melting point of 306 C.

25.6 grams of the addition salt were dissolved in 250 milliliters -N sodium hydroxide solution. The solution was diluted with water to 400 milliliters, and 7.1 milliliters glacial acetic acid were added. 22 grams of the free 3-aminomethyl-4,6-dichlorobenzoic acid were precipitated, recovered by filtration, and washed with acetone and ether (100% yield). The free acid melted at 320 C. with decomposition. The equivalent weight found was 222.6 (calculated 220.07).

A nitration mixture was prepared from 70 milliliters sulfuric acid monohydrate by dropwise addition of 8.4 milliliters fuming nitric acid (sp.gr.1.52) at 0 to 6 C. 22 grams 3-amino-methyl-4,6-dichloro-benzoic acid were added to the nitration mixture in small portions while the temperature was kept at about 40 C. After addition was completed, stirring was continued for about three hours at 50 C. The reaction mixture was cooled and then poured over 500 grams ice. A precipitate of fine particles formed in the aqueous medium. It was filtered off with suction, and was dissolved without drying in a mixture of 45 milliliters concentrated sodium hydroxide solution and milliliters water. The alkaline solution was heated to 40 C., and 11 milliliters acetic anhydride were added. The mixture obtained spontaneously heated to 50 C. It was stirred for three hours. It was then acidified with hydrochloric acid, whereby 3-acetylaminomethyl-4,6-dichloro-5-nitrobenzoic acid was precipitated. The acid was recovered by filtration, and purified by dissolutron in aqueous sodium hydroxide solution and precipitation by hydrochloric acid. The purified acid had a meltmg point of 239 C. which was raised to 240 C. by recrystallization from 50% aqueous ethanol. The yield was 27.1 grams (88.5%).

When 6.15 grams (0.02 mole) of the 3-acetylaminomethyl-4,6-dicl1loro 5 nitrobenzoic acid were hydrogenated in the presence of a palladium catalyst and then reacted with KICl as described in the preceding examples, there were obtained 9 grams 3-acetylaminomethyl-5-amino-2,4,6-triiodobenzoic acid which melted with decomposition at 230 C. and had an equivalent weight of 576 (calculated 585.9). The product was converted to 3-acetylaminomethyl-5-acetylamino-2,4,6 triiodobenzoic acid in the manner described in Example 1.

benzoic acid may also be prepared by a sequence of reactrons starting with unsubstituted benzoic acid.

250 grams benzoic acid were dissolved in 2500 milliliters concentrated sulfuric acid (sp.gr.1.84). 250 grams N-hydroxymethyl-chloroacetamide were stirred into the solution at room temperature. The solution so prepared was left to stand for three days, and was then poured over 10 kilograms ice. Upon further standing, the gelatinous precipitate originally formed crystallized. The crystals were filtered from the solution, and washed with water. They were purified by being dissolved in sodium bicarbonate solution and precipitated by hydrochloric acid. The purified material was then recrystallized to remove all residual benzoic acid. 160 grams 3-chloroacetylaminomethylbenzoic acid were obtained and had a melting point of 158-160 C. The equivalent weight found was 227 (calculated 228.5).

100 grams 3 chloroacetylaminomethylbenzoic acid were heated to a boil in 1000 milliliters 18% hydrochloric acid for 2.5 hours. Upon cooling, 64 grams of the HCl-addition compound of 3-aminomethylbenzoic acid were recovered by filtration under suction.

187 grams of the HCl-addition compound prepared in the manner described hereinabove were dissolved in 500 milliliters water, and 40 grams sodium hydroxide dissolved in 200 milliliters water were admixed to the solution. The resulting mixture was heated to 60 C., and 110 grams acetic anhydride were added with agitation in one batch. The temperature rose spontaneously to 60- 70 C., and the 3-acetylaminomethylbenzoic acid started precipitating. The reaction mixture was cooled with ice, and the precipitate was recovered by filtration. It was recrystallized from 4000 milliliters 1:1 hydrochloric acid. There were obtained 160 grams 3-acetylaminomethylbenzoic acid melting at l68-170 C.

100 grams 3-acetylaminomethylbenzoic acid were dissolved in 250 milliliters concentrated sulfuric acid, and the solution was cooled to C. A mixed nitration acid prepared from 40 milliliters concentrated nitric acid (sp.gr.1.4l) and 40 milliliters sulfuric acid was added gradually. The reaction mixture was poured over ice one hour later, and the precipitate formed was filtered off, washed, and dried. The crude product weighed 124 grams, and had a melting range of 188 to approximately 235 C. It was refluxed with 1200 milliliters ethanol for 20 minutes, and the refluxed mixture was filtered while still hot. The solids retained on the filter weighed 34 grams after drying, and consisted of 3-acetylaminomethyl-5-nitrobenzoic acid having a melting point of 266-268" C. The mother liquor mainly contained 3-acetylaminomethylnitrobenzoic acid.

9.5 grams 3-acetylaminomethyl-S-nitrobenzoic acid were suspended in 250 milliliters water containing milliliters 10% hydrochloric acid. 0.75 gram of a catalyst containing 10% Pd on a carbon support were added, and the mixture was treated with hydrogen at ambient temperature and pressure. The nitrobenzoic acid derivative quickly dissolved. When hydrogen absorption ceased, the catalyst was removed by filtration, the filtrate was diluted to 2500 milliliters, and treated with 122 milliliters N KlCl solution in the manner described in Example 1. There were obtained grams 3-acetylaminomethyl-5- amino-2,4,6-triiodobenzoic acid having a melting point of 228-230 C. The acid was further acetylated as described in Example 1.

Example 8 4-iodobenzoic acid is a suitable starting material for the synthesis of 3-acetylaminomethyl-5-acetylamino-2,4,6- triiodobenzoic acid and of its homologs.

96 grams 4-iodobenzoic acid and 100 grams N-hydroxymethyl-dichloroacetamide were subjected to a condensation reaction in 970 milliliters concentrated sulfuric acid in a manner analogous to the procedure of Example 1. There were obtained 98 grams 3-dichlor0acetylaminomethyl-4-iodobenzoic acid having a melting point of 207 C. and an equivalent weight of 389 (calculated 388). The

HCl addition compound of 3-aininomethyl-4-iodobenzoic acid was obtained in a yield of 30 grams from 38.3 grams 3'dichloroacetylaminomethyl-4-iodobenzoic acid by refluxing in a mixture of water, hydrochloric and acetic acid in a manner analogous to Example 1 yield). The free acid was obtained in a yield of practically by reaction of the addition compound with sodium hydroxide in water, and precipitation by acetic acid. It had a melting point of 282283 C.

55 grams of the 3-amiuomethyl-4-iodobenzoic acid were nitrated at 20 C. in 200 milliliters nitric acid (sp.gr.1.52), and the nitration mixture was worked up in the manner apparent from the preceding examples. The nitrated compound was acetylated as described hereinabove to form 3-acetylaminomethyl-4-iodo-5-nitrobenzoic acid which melted at 198-200 C. after purification.

21.8 grams (0.58 mole) 3-acetylaminomethyl-4-iodo- 5-nitrobenzoic acid were hydrogenated in 500 milliliters methanol in the presence of 3.1 grams Raney nickel catalyst. The amount of hydrogen necessary for hydrogenation of the N0 radical (3.8 liters) was absorbed. The catalyst was removed by filtration. Only trace amounts of iodine ions were found in the filtrate, indicating that very little of the iodine bound to the benzene nucleus had been hydrogenated. The filtrate was evaporated to dryness, and the residue was dissolved in aqueous hydrochloric acid. The acid solution was filtered. The filtrate was diluted with water to six liters, and was gradually mixed with milliliters N KICl solution. When the reaction mixture was worked up in analogy to Example 1, there were obtained 21.5 grams 3-acetylaminomethyl-5-amino-2,4,6- triiodobenzoic acid. Further acetylation yielded 3-acetylaminomethyl-S-acetylamino-2,4,6-triiodobenzoic acid.

Example 9 81.7 grams of the monomethyl ester of S-nitroisophthalic acid (3-methylcarboxy-5-nitrobenzoic acid) were heated :barely to boiling temperature in a large excess of thionyl chloride for one hour. The excess of thionyl chloride was then removed by distillation, and the residue was recrystallized from hexane. 84.5 grams 3-methylcarboxy-S-nitrobenzyl chloride were obtained (93.5% yield).

One gram-atom magnesium chips was refluxed for six hours with agitation in a mixture of 230 milliliters absolute ethanol and 6.2 milliliters carbon tetrachloride. The resulting magnesium ethylate was mixed with milliliters (one mole) diethyl malonate and 228 milliliters chloroform. The mixture was heated to 80 C. for 2% hours. The solutions were then distilled off in a vacuum. The residue consisting essentially of was dissolved in milliliters chloroform. The solution was mixed under agitation with a solution of 140 grams (0.575 mole) 3-methylcarboxy-S-nitrobenzoyl chloride in 180 milliliters chloroform. The benzoyl chloride derivative had been prepared as described in the preceding paragraph. The reaction mixture was heated to 40 C. for one hour, and was then cooled to 35' C. 323 milliliters 21% sulfuric acid were admixed at this stage.

The mixture separated into an aqueous and an organic solvent layer. The latter was separated from the aqueous layer, was washed with water and sodium bicarbonate solution, dried, and then evaporated to remove the organic solvents. An oily residue of (3-methylcarboxy-5- nitro-benzoyl) -bis (ethylcarboxy -methane was obtained. It was heated to 120-130 C. for eight hours in a mixture of 200 milliliters glacial acetic acid, 140 milliliters water, and 24 milliliters concentrated sulfuric acid. Ethyl acetate formed during the reaction and was continuously distilled off. After completion of the reaction, the residue was stirred into 100 grams ice water. A crystalline product precipitated, and was filtered off, washed, and recrystallized from much water or methanol. It also could be purified by dissolution in sodium bicarbonate solution and 13 precipitation with acid. There were obtained 81.5 grams 3-carboxy-5-nitro-acetophenone having a melting point of 90 C.

25 grams 3-carboxy-5-nitroacetophenone were dissolved in 250 millilters 5% aqueous sodium bicarbonate solution, and mixed with a dispersion of 9.12 grams sodium borohydride in 20 milliliters water. The solution which formed after a few hours was diluted with water and acidified with hydrochloric acid. A precipitate formed. It was filtered ofi, washed, and dried. 21.4 grams 3-tx-hydroxyethyl-5-nitnobenzoic acid having a melting point of 169-- 172 C. were obtained.

12.6 grams of 3-a-hydroxyethyl-S-nitrobenzoic acid were admixed in small portions to a solution of 15 milliliters concentrated sulfuric acid in milliiiters acetonitrile. The resulting mixture was kept at a temperature not exceeding 30 C. for three days while it was being stirred. It was then admixed to 300 grams crushed ice. There were obtained 10 grams 3-ocacetylaminoethyl-5-nitro benzoic acid. Melting point 225-227 grams.

50.2 grams (0.2 mole) 3-a-acetylarninoethyl-S-nitrobenzoic acid were prepared as described in the preceding paragraphs, and were hydrogena ed at ambient pressure in two liters 0.1 N aqueous sodium hydroxide solution in the presence of 10 grams 10% palladium-carbon catalyst. After an amount of hydrogen sufiicient for reduction of the nitro radicals was absorbed, the catalyst was removed by filtration, the filtrate was acidified, diluted with water to liters, and mixed with 177.5 grams 44% iodine chloride. The mixture was agitated for 30 hours at 50 C.

The precipitate which formed upon cooling of the reaction mixture was filtered off, washed, dissolved in dilute ammonium hydroxide solution, and reprecipitated by means of a mineral acid. 71.5 grams of 3-a-acetylaminoethyl-5-a-mino-2,4,6-triiodobenzoic acid were obtained, and had a melting point of 199 to 203 C.

A few drops of concentrated sulfuric acid were added to a mixture of 30 grams S-a-acetylaminoethyl-S-amino- 2,4,6'triiodobenzoic acid in 200 milliliters acetic anhydride to initiate a reaction which was brought to completion by heating on a steam bath for three hours. The excess acetic anhydride and the acetic acid formed during the reaction were distilled off. The distillation residue was triturated with a small amount of water to induce crystallization. The crystalline product was filtered off. It was purified by dissolution in dilute ammonium hydroxide solution and precipitation with dilute hydrochloric acid containing a little sodium bisulfite, washing, and drying. There were obtained 22 grams 3-a-acetylaminoethyl-5- acetylamin-o-2,4,6-triiodobenzoic acid which melts at approximate y 200 C. with decomposition.

The sodium and lithium salts of the acid are readily soluble. The N-methylglucamine salt and the diethanolamine salt have even greater solubility. The N-methylglucamine salt is miscible with water in practically all proportions.

Example 10 35.1 grams (0.06 mole) 3-acetylaminomethyl-S-amino- 2,4,6-triiodobenzoic acid were mixed with 180 milliliters formic acid, and the mixture was heated to 50 C. 0.25 milliliter concentrated sulfuric acid were then added, and the mixture was agitated for 90 minutes while its temperature was maintained at 50 C. The reaction mixture was cooled, and a precipitate was filtered off. The precipitate was dissolved in 300 milliliters 3% aqueous sodium bicarbonate solution and the solution was filtered to remove innsolub-le material. Upon acidification with hydrochloric acid, crude 3-acetylaminomethyl-S-formylamino-2,4,6-triiodobenzoic acid was precipitated. It was recovered by filtration, washed, and dried, and had a melting point of approximately 244-245 C. with decomposition.

The acid was further purified by conversion to the cyclohexylamine salt. 16.8 grams crude 3-acetylaminomethyl-5- formylamino-2,4,6-triiodobenz0ic acid and 3 milliliter cyclohexylamine were dissolved in 15 milliliters methanol, and the salt formed thereby was precipitated from the methanol solution with ether. It was then dissolved in water, and the aqueous solution was filtered to remove insoluble impurities. The filtrate was acidifiied to precipitate the purified acid which was filtered off nad dried.

The purified 3-acetylaminomethyl-S-formylamino-2,4,6- triiodobenzoic acid has a melting point of 245-246 C. (decomp) and was found to have an equivalent weight of 612 (calculated 613.9).

One gram 3-acetylaminomethyl-S-formylamino-2,4,6- triiodobenzoic acid is soluble at the boiling point in about 3 milliliters methanol, 50 milliliters ethanol, or in 15-16 milliliters dioxane. The acid is practically insoluable in ethyl ether. The sodium and N-methylglucamine salts are soluble in water to approximately grams per milliliter of solution.

The water soluble salts of the 3-lower-alkanoylamidolower alkyl-5-lower-alkanoylamido-2,4,6-triiodenbenzoic acids of the invention are suitable for intravenous injection in aqueous solution for urography, angiography, and angiocardiography. The water insoluble esters may be employed in salpingography and in the X-ray investigation of other body cavities which are directly accessible from the outside for the instillation of a contrast medium. Mixed aqueous solutions containing 40 to 60 percent of the N-methylglucamine salt and 5 to 10 percent of the sodium salt of 3-acetylaminomethyl-5-acetylamino-2,4,6- triiodobenzoic acid have been found to be particularly advantageous for urography. 10 to 30 minutess after intravenous injection of such a mixed solution, sharply defined X-ray pictures of the urinary tract may be taken.

Mixed aqueous solutions of 6580| percent of the N- methylglucamine salt and of 2 to 6 percent of at least one physiologically tolerated alkali metal salt of 3-a-ace- 'tylaminoethyl 5 acetylamino 2,4,6-triiodobenzoic acid have been found to produce very good angiograms and angiocardiograms.

The following examples are illustrative of contrast medium formulations containing the compounds of the invention as radioopaque constituents, and adjuvants not necessarily novel in themselves, and performing known functions.

Example 11 The following formulation of an injectable aqueous solution has been found suitable for urography:

Grams 1. 3-acetylaminomethyl-S-acetylamino-2,4,6-triiodobenzoic acid 47.7 2. N-methylglucamine 12.87 3. Sodium hydroxide 0.4

4. Disodium salt of ethylenediaminetetraacetic acid (EDTA) 5. Double distilled water to make milliliters.

Example 12 The following aqueous contrast medium was found suitable for angiography and angiocardiography:

Grams 1. 3-acetylaminomethyl-5-acetylamino-2,4,6-triiodobenzoic acid 59.95 2. N-methylglucamine 16.32 3. Sodium hydroxide 0.5 4. Disodium salt of EDTA 0.04

5. Double distilled water to make 100 milliliters.

1 5 The several components of the injectable solution were combined in the same maner as described in Example 11. The finished solution was clear, sterile, and had a pH of 7.1 :0.2.

Example 13 The solution was made up in a manner analogous to the procedure described in Example 1.

Example 14 A colloidal suspension of a radioopaque material of the invention was made for use in bronchography and hysterosalpingography to the following formulation:

Grams 1. 3-acetylaminomethyl-5-acetylamino-2,4,6-triiodobenzoic acid 381.4 2. N-methylglucamine 118.6

3. Sodium carboxymethyl cellulose (CMC), high viscosity 23.5 4. Methyl p-hydroxybenzoate 0.7 5. Propyl p-hydroxybenzoate 0.3 6. N -bromoacetylnicotinamide 1.0 7. 96% ethanol 28.0

8. Double distilled water to make 1000 milliliters.

The p-hydroxybenzoates were dissolved in the alcohol. The CMC was moistened with this alcoholic solution whereupon it was mixed with about 500 milliliters water. The mixture was heated to 6070 C. while mixing continued until a homogeneous gel free from solid particles was obtained.

The iodobenzoic acid derivative was dissolved in 240 milliliters water at 6070 C. by means of the N-methylglucamine. The aqueous solution was filtered. The filtrate had a pH of 7.2-7.7.

The N -bromoacetylnicotinamide was separately dissolved in about 5.5 milliliters hot water.

The gel, the aforementioned filtrate, and the last mentioned solution were combined, and the total volume was adjusted to 1000 milliliters with the remainder of the water. The resulting mixture was homogenized on a colloid mill and bottled. The bottles and their contents were sterilized in live steam at 105 C. for 30 minutes.

Example 15 Another colloidal suspension for use in bronchiography and hysterosalipingography was made up to the following formula:

Grams 1. 3 acetylaminomethyl 5 acetylamino 2,4,6-

triiodobenzoic acid 381.4 2. N-methylglucamine 118.6 3. Cinchonine hydrochloride 1.0 4. CMC, medium viscosity 15.0 5. Methyl p-hydroxybenzoate 0.7 6. Propyl p-hydroxybenzoate 0.3 7. Ethanol, 96% 50 8. Double distilled water to make 1000 grams.

The p-hydroxybenzoates were dissolved in the alcohol, and the CMC was moistened with the alcoholic solution. The moistened CMC was then homogenized with 300 milliliters of boiling water to produce a smooth gel.

The triiodobenzoic acid derivative and the cinchonine hydrochloride were dissolved in 350 milliliters boiling water in the presence of the N-methylglucamate, and the solution so produced was combined with the previously mentioned gel. A uniform mixture was produced by stirring, and the volume was adjusted to 1000 milliliters wtih the balance of the water. The diluted solution was filtered and sterilized.

Example 16 A suspension of an ester of the invention was formulated for bronchography, and for visualizing the mucous membranes of the stomach in relief:

1. Ethyl 3 acetylaminomethyl-S-acetyl-amino-2,4,

6-triiodobenzoate grams 50.00 2. Pure glucose do 34.16 3. CMC, medium viscosity do 7.00 4. Tween 20 (a commercial emulsifying agent and detergent which is a sorbitan monolaurate polyoxyalkylene derivative) do 5.00 5. Methyl p-hydroxy-benzoate do 0.52 6. Propyl p-hydroxybenzoate do 0.22 7. Benzyl alcohol -do 0.25 8. 96% ethanol milliliters 4 9. Double distilled water to make 100 milliliters.

A gel was first prepared from the CMC, the alcohol, the p-hydroxybenzoates, the glucose, and a little water. The Tween 20 and ultimately the triiodobenzoate derivative Were then admixed to the gel in small batches. The mixture obtained was diluted with water to 100 milliliters, and homogenized mechanically. The viscosity was adjusted to a desired value by addition of the benzyl alcohol. The finished suspension had a specific gravity of 1.28, and was bottled under sterile conditions.

It will be appreciated that the formulations of Examples 11 to 16 are merely illustrative of the manner in which the salts and esters of the several acids of the invention may be employed. The salts and lower alkyl esters of the other 3-(oc-lOW6l' alkanoylamino)-lower alkyl-S-lower alkanoylamino-2,4,6-triiodobenzoic acids with the bases mentioned in Examples 11 to 16, and the salts of other physiologically tolerated bases with the triiodobenzoic acid derivatives of the invention are employed in an analogous manner, and produce similar results. Suitable organic bases other than those specifically referred to hereinabove include morpholine, lysidine, and such additional alkanolamines as aminopropanediol, N-methylaminopropanediol, dipropanolamine, and aminobutanol. The organic base components of the radioopaque salts of the invention have merely the function of making the salt water soluble. They do not contribute to the effect produced, and are therefore not critical beyond their ability to promote solubility. They must not be toxic.

The same criteria apply to the cationic components of the inorganic salts of the invention. The potassium salts are readily prepared, but they are toxic in the concentrations necessary to produce sufficient contrast for X-ray examination. The lithium and sodium salts thus constitute the physiologically tolerated common alkali metal salts.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not limited thereto, but is to be construed broadly and restricted solely by the scope of the appended claims.

We claim:

1. A radioopaque compound of the formula wherein R and R are lower alkanoyl radicals, R" is a member of the group consisting of hydrogen and lower alkyl, and X is a member of the group consisting of hydrogen, physiologically tolerated alkali metal, lower alkyl, and physiologically tolerated alkanolamine.

a 4. A compound as setforth in claim 1, wherein R and R are acetyl, and R is hydrogen.

5. A compound as set forth in claimI, wherein R and R are propionyl, and R" is hydrogen.

6. A compound as set forth in claim 1, wherein R and R are butyryl, and R is hydrogen.

7. A compound as set forth in claim 1, wherein X is hydrogen.

8. A compound as set forth in claim 1, wherein X is sodium.

9. A compound as set forth in claim 1, wherein X is N-methylglucamine.

10. 3-acetamidomethyl 5 acetamido-2,4,6-triiodobenzoic acid.

11. The sodium salt of 3-acetamidomethyl-5-acetamido- 2,4,6-triiodobenzoic acid.

12. The N-methylglucamine salt of 3-acetamidomethyl- 5-acetamido-2,4,6-triiodobenzoic acid.

13. A water soluble physiologically tolerated salt of a radioopaque compound of the formula COOH wherein R and R are lower alkanoyl radicals.

14. An injecta'ble aqueous solution containing 40 to 80 percent N-methylglucamine 3-acetamidomethyl-5-acetamido-2,4,6-triiodobenzoate.

15. A compound of the formula CODE R-NH-OH NH-R' which comprises reacting a benzoic acid compound of the formula with an N-hydroxymethylacylamide to form the compound COOH 18 hydrolyzing the last mentioned compound until the acyl radical is replaced by hydrogen; nitrating the hydrolyzed compound to form the nitro compound acylating said nitro compound, to replace one of the hydrogen atoms in the amino radical with the radical R; hydrogenating the acylated nitro compound to reduce the nitro radical to another amino radical; iodating the hydrogenated acylated nitro compound by reacting the same with an iodating agent selected from the group consisting of iodine chloride and alkali metal iodochloride until the positions 2, 4, and 6 of the benzene ring in the benzoic acid compound are occupied by iodine; and acylating said other amino radical to replace one of the hydrogenatoms of said other amino radical with the radical R; in said formulas R and R being lower alkanoyl radicals, and Y and Y being each selected from the group consisting of hydrogen, chlorine, and iodine.

17. A method as set forth in claim 16, wherein the acyl radical of said N-hydroxymethylacylamide is selected from the radicals of a group of acids consisting of monochloroacetic acid and dichloroacetic acid.

18. A method as set forth in claim 16, wherein said nitro compound and said other amino radical are acylated respectively by reaction with anhydrides of the acids R0H and ROH.

19. A method as set forth in claim 16, wherein one of said Y and Y is iodine and the other one is hydrogen.

20. A method as set forth in claim 16, wherein said Yand Y are hydrogen.

'21. A method as set forth in claim '16, wherein one of said Y and Y' is hydrogen, and the other one is chlorine, said chlorine being replaced by hydrogen during the hydrogenating of said acylated nitro compound.

22. A method as set forth in claim 16, wherein Y and Y are chlorine, and are replaced by hydrogen during the hydrogenating of said acylated nitro compound.

23. A method as set forth in claim 18, wherein the acyl radical of said N-hydroxymethylacylamide is selected from the radicals of a group of acids consisting of monochloroacetic acid and dichloroacetic acid, and at least one of said Y and Y is chlorine and the remainder of said Y and Y is hydrogen, said chlorine being replaced by hydrogen during the hydrogenating of said acylated nitro compound.

24. In a method of preparing a compound of the formula A--NH(IJH NH:

All:

wherein Alk is lower alkyl, and A is hydrogen or lower alkanoyl, the step of reacting a compound of the formula with an iodating agent selected from the group consisting of iodine chloride and alkali metal iodochloride.

(References on following page) References Cited UNITED STATES PATENTS Hecht et a1. -2-" 167-95 Ellzey 167-95 Lyding 260518 Dreyfuss 260---518 20 3,014,063 12/1961 McLane etal 260-471 3,178,473 4/1965 Holtermann et a1. 260519 'LORRAINE A. WEINBERGER, Primary Examiner.

: F. CACCIAPA'GLIA, 111., Examiner. V.

L. A. THAXTON, V. C. CLARKE, Assistant Examiners. 

1. A RADIOOPAQUE COMPOUND OF THE FORMULA 